Synthesis and characterisation of cellulose/silica hybrids obtained by heteropoly acid catalysed sol–gel process

Cellulose/silica hybrids (CSHs) were synthesized by a sol–gel method using eucalyptus bleached kraft pulp as cellulose source and tetraethyl orthosilicate (TEOS) as the silica precursor in the presence of heteropoly acids (HPAs) as catalysts. HPAs, and especially tungstophosphoric acid H3PW12O40, showed better catalytic efficiency than conventional mineral acids. Silica was deposited on fibres in the form of a thin film or mesoparticles as revealed by SEM/EDS and AFM analyses. Roughly 40–60% of silica was incorporated into cellulosic material considerably diminishing its hydrophilicity and improving thermal stability. CSHs were structurally characterised by FTIR, 13C and 29Si solid state NMR. It was suggested that proportions of Q2, Q3 and Q4 structures in silica counterpart depended on the synthesis conditions (H2O/TEOS molar ratio and catalyst concentration among others). A clear relationship between the thermal stability of CSH and the degree of silica crosslinking in hybrids has been observed.